What is magnetic shielding

- Aug 11, 2020-

Magnetic shielding means that two media with different permeability are put into the magnetic field, and the magnetic field at their interface will undergo a sudden change, at which time the magnitude and direction of magnetic induction intensity B will change, that is to say, the refraction of the magnetic induction line will be caused.

When the magnetic sensing lines enter the iron from the air, they deviate a lot from the normal line, so there is a strong convergence effect, thus forming the magnetic shielding.

A good magnetic shield design involves the machining process, which can provide the required structure and characteristics. In the past, most magnetic shields were cut, punched, molded, and welded using standard chip metalworking techniques. Since 2012, the use of advanced laser cutting system, individual parts of the shear and computerized digital control punching have been replaced by one-step laser cutting technology. One-step machining of the main shielding elements allows faster machining times and lower machining costs without the need for high-cost machining methods. This process provides greater flexibility for shield designers, especially for profiles and special equipment such as specialized cutting and serialization.

A static magnetic field is a magnetic field produced by a steady current or permanent magnet. Magnetostatic shielding is made of ferromagnetic material with high permeability to shield the external magnetic field. It has similar but different effects with electrostatic shielding.

The principle of magnetostatic shielding can be explained by the concept of magnetic circuit. If the ferromagnetic material is made into a circuit with a cross section as shown in the figure above, the vast majority of the magnetic field is concentrated in the ferromagnetic circuit in the external magnetic field. The ferromagnetic material can be analyzed as a parallel magnetic circuit with the air in the cavity. Because the permeability of a ferromagnetic material is several thousand times greater than that of air, the reluctance of a cavity is much greater than that of a ferromagnetic material, and the vast majority of the magnetic induction lines of the external magnetic field will pass along the walls of the ferromagnetic material, with very little flux entering the cavity. In this way, the cavity shielded by ferromagnetic material basically has no external magnetic field, so as to achieve the purpose of magnetostatic shielding. The higher the permeability of the material, the thicker the tube wall and the more significant the shielding effect. Because commonly used magnetic permeability high ferromagnetic materials such as soft iron, silicon steel, permalloy do shielding layer, so static magnetic shielding is also called ferromagnetic shielding.

Magnetostatic shielding is widely used in electronic devices. For example, magnetic flux leakage from transformers or other coils can affect the motion of electrons and affect the focusing of electron beams in oscilloscopes or picture tubes. In order to improve the quality of the instrument or product, it is necessary to implement magnetostatic shielding for the components that produce magnetic flux leakage. In the watch, in the movement of the cover with soft iron thin shell can play an antimagnetic effect.

As noted above, the electrostatic shielding effect is very good. This is because the conductivity of a metal conductor is a dozen orders of magnitude greater than that of air, while the difference between the permeability of a ferromagnetic substance and air is only a few orders of magnitude, usually about a few thousand times greater. So there's always some flux leakage in a magnetostatic shield. In order to achieve better shielding effect, multi-layer shielding can be used to screen out the residual magnetic flux leaking into the cavity again and again. So magnetic shielding that works well is usually bulky. But to create an absolute "magnetostatic vacuum", the Meissner effect of superconductors could be used.